Patent Document 1 discloses a pneumatic radial tire as related conventional art of this kind.
In the pneumatic radial tire, a portion that protrudes most in the tire-width direction, i.e., the widest portion is located in a sidewall portion on the vehicle-fitted outer side. The rubber gauge (the thickness of the rubber measured from the external surface of the tire to a carcass layer) of the widest portion is designed to be smaller than the rubber gauge of a widest portion in a sidewall portion on the vehicle-fitted inner side.
The pneumatic radial tire with the above-described configuration is made lighter in weight and reduces the transmission of a noise to the passenger compartment, the noise being generated at a tread portion during running.    Patent Document 1: JP-A Hei 8-156532